Lyme disease is the most common vector borne infectious disease in North America and Europe. It is a progressive disease with a wide array of clinical manifestations. Treatment of early infection is highly effective, and early diagnosis and treatment are critical to prevent disease progression. By contrast, disseminated late- phase infection is associated with debilitating, sometimes, permanent damage to the nervous and musculoskeletal systems and can be refractory to antibiotics. Currently the laboratory diagnosis of Lyme disease is based on the detection of antibodies against Borrelia burgdorferi in a two-tier serological assay. However, serological assays using native or recombinant proteins from B. burgdorferi as antigens are often insensitive for the detection of antibody present at the time many patients with early Lyme disease usually seek initial medical care and/or lack sufficient specificity as both native and recombinant B. burgdorferi protein antigens contain B cell epitopes that cross react with antibodies against other bacterial species. As a result, it has been estimated that current IgM or IgG Lyme disease assays fail to diagnose early disease in patients ~50% of the time. The failure of serological assays to consistently identify B. burgdorferi infection in patients with suspected Lyme disease necessitates the development of a new class of diagnostic tests. The QuantiFERON(R) assay is a cellular-based IFNg release assay for the detection of antigen-specific T cells in the blood of patients infected with Mycobacterium tuberculosis. This assay, which detects the production of the proinflammatory cytokine IFN? in response to stimulation with peptide antigens derived from M. tuberculosis, has proven to be highly sensitive and highly specific in the diagnosis of tuberculosis, supplanting ineffective serological assays and improving upon diagnosis using the tuberculin skin test. A cellular based assay would represent a new direction in the development of diagnostic assays for Lyme disease, with the potential for being significantly more specific and sensitive than current serological assays. However, the development of such an assay requires the identification of highly-specific peptide epitopes unique to B. burgdorferi. The goal of the current study is to identify unique T cell-epitopes derived from B. burgdorferi proteins for use in a QuantiFERON(R)-based cellular assay for the diagnosis of Lyme disease.